1. Field of the Invention
The present invention relates generally to apparatus for coaxially mounting a cylindrical body to a rotatable shaft and more particularly to compression coupling apparatus for securely affixing a conveyor pulley to a rotatable shaft in which the shaft and/or pulley end plate need not be in perfect alignment.
2. Description of the Prior Art
Mounting of pulleys on rotatable shafts has presented universal problems. Of course, welding the pulley to the shaft is one of the simplest mounting methods. Removal of the shaft, however, is impractical and if care is not exercised in the welding, misalignment can occur. Another prior art device uses keys and set screws. Keyways are cut in each of the pulley end plates. Following insertion of the shaft and keys, two pair of set screws are threaded into the end plates. The first pair of set screws engage the keys and the second pair engage the shaft. A major problem with this device is that a high degree of accuracy is required in the installation of the end plates such that the keyways are aligned and the bores are coaxial. Any misalignment of the keyways makes installation of the keys much more difficult or impossible. (This problem can be aggravated by keyway misalignment in the shaft.) If the bores are not perfectly coaxial, bending of the shaft will result, causing vibration, fatigue of the bearings, and the associated parts, and increasing run out. In addition, the set screws mark the shaft and are ineffective in preventing lateral movement, or creeping of the pulley on the shaft.
Another prior art device of mounting a pulley to a rotatable shaft uses a pair of frustum-shaped collets. Each collet is bored axially to accommodate the shaft and is slotted, permitting the collet to be compressed around the shaft to prevent creeping of the pulley along the shaft. The collet and shaft also contain keyways designed to accept a key which prevents rotation of the shaft in the collet. Each of the pulley end plates contains a tapered bore converging toward the center of the pulley, the tapered bore being designed to mate with the collet along its entire tapered surface. Along the juncture of the collet and the end plate are a number of threaded mounting holes. The holes are bored into the end plate deeper than the collet and are threaded in the end plate only.
After the shaft is inserted into the pulley, the key and collet are installed on the shaft and the collet pressed into the end plate, the mounting bolts are threaded into the mounting holes. The bolt threads engage the end plate threads, and the bolt ends seat against the bottom of the bores in the collet. Finally, the collet is struck (such as with a hammer and drift punch) while the bolts are tightened.
It should be appreciated that if the end plates are misaligned with respect to the shaft, the collet will at first mate with the end plate at only two points, which provides insufficient compression to prevent creeping of the pulley along the shaft. If the bolts are tightened further, the collet will be forced into alignment bending the shaft, which can cause run out at the pulley face or shaft breakage. Additionally, keyway alignment is still critical in this device. Thus, although this hub-mounting device greatly reduces creeping of the pulley along the shaft, it does not prevent the vibration and fatigue caused by bending of the shaft.
A different device for coaxially mounting a pulley to a shaft is disclosed in my earlier U.S. Pat. No. 3,905,209 entitled "Compression Hub Apparatus for Mounting a Cylindrical Body to a Rotatable Shaft". Attached to each end of the pulley is an end plate having a first bore axially aligned with the pulley of suitable diameter for receiving the shaft. A second, larger diameter bore, coaxial with the first, extends a short distance into each end plage forming cylindrical recesses. Each recess is enclosed by a cover plate attached by suitable bolts. In a first embodiment a plurality of compressible cup-shaped discs, each having a diameter corresponding to the diameter of the recess and a bore suitable for fitting over the shaft are disposed within each cavity. As the bolts mounting the cover plate are tightened, the cover plate is drawn toward the end plate deforming the discs which are thus caused to engage both the shaft and the walls of the cavity locking the pulley to the shaft. In another embodiment the locking device resembles an oblique helicoid having a cross section similar to a parallelogram with the shorter sides paralleled to the axis of the helicoid forming a shaft gripping inner surface and a cavity gripping peripheral surface. The helicoid is similarly deformed within the cavity by the cover plate.